I support a bunch of software developers running CentOS 6.9, and NVIDIA quadro NVS 440 video cards running 3 monitors. One user wanted to run his monitors in portrait mode and Xinerama seemed to be blocking it. I disabled Xinerama and he was then able to use portrait mode.

However he was no longer able to move things between monitors - anything opened in one window stays in that window.

Are there some other options I need to be looking at, in /etc/X11/xorg.conf (or somewhere else for that matter)?